Semiconductor integrated circuits are known in the art. Typically, integrated circuits include a package which contains one or more substrates or “dies”. The substrates may be provided with electronic circuits and be provided with pads via which the substrates (and the electronic circuits) can be connected to the outside world, e.g. via bond-wires that are connected to pins which extend from the package inside to the exterior of the package.
However, a general problem is that current may be injected into the substrate, for example when a pad is driven below or above the supply voltage, which may affect the operation of the electronic circuit.
In order to prevent the injected current from affecting the operation, it is known to implement a so called “guard ring” which shields the electronic circuit from the injected current. For example, U.S. Pat. No. 5,168,340 describes a passive latch-up protection improvement in which polysilicon lines cross or cut a guard-ring around a logic circuit. When an amount of injected current exceeds a certain magnitude, latch up of the transistors in the logic circuit occurs and the transistors are shut off.
German patent application publication DE199 58 204 A1 discloses an integrated circuit provided with a sensor which senses the voltage of a pin and a transistor which is controlled by the sensor to block the connection between the pin and a core part of the integrated circuit when the voltage exceeds a first voltage threshold or comes below a second voltage threshold.
However, this does not provide a protection of the core part to currents flowing from the pin to the core part via other paths than the connection. In addition, if despite the blocked connection the core part is subject to an injected current, the operation of the core part can be affected in an unpredictable manner. Furthermore, since the path from the pin to the core parts is cut, a normal functioning of the device is no longer possible.